Background

The site borehole information demonstrates that the sediments are sitting on the top of Ignimbrite and there is also fractured Ignimbrite weathered with the content of clay is located at the bottom.

Purpose

The study was made to determine the sedimentary thicknesses as well as to obtain the contact between high resistivity values associated to Ignimbrite and low resistivity values associated with Ignimbrite fractured and weathered with the content of clays.

Streaming-potential (SP) is an electrical surveying method used when fluids or electrolytes—typically water—move through porous areas in the the ground. This creates a change in voltage that can be read using a voltmeter and two electrodes.

Before we dive into details, let’s start with a primer on three different terms that are abbreviated “SP.” In this article, we’ll be discussing self-potential, which is synonymous with spontaneous-potential. The self-potential method in geophysics refers to an electrical surveying method used for looking at electrical anomalies in the ground. It is primarily used in mineral exploration. Streaming-potential, on the other hand, is caused by a fluid —typically water with dissolved minerals (an electrolyte)—moving in the ground, which causes a change in voltage.

The Oroville Dam failure highlights a growing concern in the United States.

This morning, CBS News reported that the United States has 85,000 dams and levees. Most of those were designed and constructed in the 1950's through the 1960's and are now past due and are in danger of failing.

One-dimensional (1D) resistivity surveys are not ideal because they assume that the geological layers are horizontal and homogeneous—which is rarely the case. Two-dimensional (2D) resistivity surveys are an improvement but still an approximation, as they assume the geology continues infinitely in both directions perpendicular to the survey line.

The three-dimensional (3D) time-lapse resistivity survey is the holy grail of resistivity surveys. It is an extremely accurate and effective method that allows you to not only see the surveyed area in three dimensions—but also how the resistivity in the surveyed area changes over time.

Induced polarization (IP) is the Earth’s capacity to hold an electric charge over time. IP measures the voltage decay curve after the injected current is shut off. The higher the IP, the longer over time the charge is held—IP decays over time, typically a few seconds but sometimes up to minutes, and will eventually disappear. IP is especially useful for mineral exploration applications.

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Dr. Keith N. Muhlestein, PG, REM, from the University of Texas at San Antonio’s Environmental Science and Engineering department, used AGI equipment for an electrical resistivity survey to image Karst regions within Friesenhahn Cave in Texas.